Posted by: Jim (jwelborn@lexcominc.net) on Sun Dec 10 09:05:57 2006

> >>> If its true that stride length is directly related to bat speed then one must assume that shorter stride means less bat speed. There are lots of short striders and no striders that generate great bat speed. One can easily measure stride length on swing analysis software and see that stride length is not necessarily what causes weight transfer. Weight transfer is directly related to hip slide. There are some no striders who have just as much hip slide as striders (Jim Edmonds is one example). There is much more at work here than stride length. <<<
>
> Hi Jim
>
> During hip slide, the hips are in line with the direction they are sliding. Would you say that as hip slide slows to a stop, the linear momentum of the hips is transferred into angular momentum that induces hip rotation?
>
> Try this test. – Slide your hips into a wall. Without engaging the muscles in the pelvic area, you will find there in no hip rotation induced as the hip’s momentum is expended into the wall. The physics principles that govern bat rotation also govern hip rotation.
>
> Your thoughts Jim
>
> Jack Mankin



Jack,

You are correct. Linear hip slide in itself does not change into hip rotation unless the pelvic muscles coordinated with the legs induce and build rotation. Hip rotation begins before the hips stop sliding and hip slide ends well before the hips stop rotating. If this is true, then hip rotation does indeed BEGIN as “the back hip rotating around the front hip. But it DOES NOT END that way. As hip slide decays and hip rotation builds, the axis which first establishes itself near the front hip, moves to the spine. I believe linear hip slide in no way hinders hip rotation when correctly done.

Swing analysis software supports this theory of overlapping hip slide/hip rotation. I looked at 9 good batters (one 7th grade fastpitch, two varsity HS fastpitch, one D1 college fastpitch, two Olympic fastpitch, and three major leaguers- A. Rod, Pujols, & Sosa). EVERY example showed overlap. The overlap ranged from two to four video frames. In other words, hip rotation began BEFORE hip slide ended. Granted, two to four frames is not much time (2/60 to 4/60 of a second). So let’s put that into perspective. The time it takes for the bat to travel 180 degrees from launch to contact varies from six to nine frames in this group with the pros being faster. (The pros were 6 frames, the Olympic and HS were 7-8 frames and the 7th grader was 9 frames).

How much time elapsed between the end of hip slide and the end of hip rotation? In this group it ranged from eight to twelve video frames (8/60 to 12/60 of a second).

Hip slide creates weight transfer. Weight transfer toward the front side allows the back foot to become unweighted and is the only way spinning on the back foot and “squashing the bug” can be avoided. With some individuals, hip slide is a flexible movement. That is, flexibility in the lumbar (lower spine) area can be readily observed. With others it is less flexible. That is, the lumbar area appears to be more rigid.

The axis of rotation must acquire a proper relationship with the line of the pitch. The axis of rotation should be 90 degrees to the line of the pitch (when viewed across the plate from the batter). The closer the axis of rotation is to the 90 degree relationship, the more efficiently the energy of rotation can transfer to the bat and keeping the bat on the line of the pitch becomes automatic. When the relationship is wrong, the batter will either swing up or down through the line of the pitch (hitting through a short zone) or will attempt to compensate with the arms which will cause disruption of transfer of rotational energy.

With more flexible individuals, the hips will travel further forward than the upper torso during weight transfer before the onset of rotation. Individuals who exhibit a more upright stance and negative move must have this flexibility or the axis of rotation will fail to achieve the correct posture. Likewise, no-striders need this lumbar flexibility.

Less flexible individuals will attain the proper axis posture during the negative move. Their hip slide will be accompanied with more forward movement of the upper torso during weight transfer.

Swinging a bat is a complex interaction of parts of the entire body. It is difficult and sometimes erroneous to study or describe one specific part without considering its dynamic relationship with the other parts.

Jim